Antagonistic Activity of <i>Bacillus velezensis</i> OEE1 Volatiles Against <i>Biscogniauxia mediterranea</i>

Increase in olive tree diseases caused by the wood-borne fungus, Biscogniauxia mediterranea, is a cause for concern. Given the importance of this plant in Mediterranean countries, the search for sustainable disease control measures is essential. The strain OEE1 of Bacillus velezensis was selected to evaluate the potential growth inhibitory effect of its volatile organic compounds (VOCs) against the fungus, using the sandwich plate technique, in which two bottoms of Petri dishes (one containing the bacterial culture and the other the fungal pathogen) are sealed together, allowing only VOCs to mediate the interaction with the pathogen. Results showed that the bacterial VOCs had a strong antagonistic activity against the fungus, achieving an 81.76% inhibition rate and inducing microscopic alterations in the fungal mycelium. The germination of B. mediterranea spores was completely blocked upon exposure to VOCs from B. velezensis. At the end of the experiment, extensive spore lysis was observed. The antagonistic potential was further assessed on detached olive twigs to evaluate its effect on necrosis following artificial inoculation with B. mediterranea. This preliminary study provides valuable insights into the potential use of VOCs from B. velezensis OEE1 as effective biocontrol agents against charcoal canker disease in olive trees.